KARACHI, Jan 18 - Firefighters in Pakistan's largest city were fighting to extinguish a massive blaze on Sunday that has killed six people and reduced parts of a shopping mall to rubble in Karachi's historic downtown.

Videos showed flames rising from the building as firefighters laboured through the night to stop the fire from spreading in the dense business district. Hundreds of people had gathered around the building, including distraught store owners whose businesses had turned to ash.